This paper presents a low-complexity energy efficient channel pre-processing update scheme, targeting the emerging 3GPP long term evolution advanced (LTE-A) downlink. Upon channel matrix renewals, the number of explicit QR decompositions (QRD) and channel matrix inversions are reduced since only the upper triangular matrices R and R^-1 are updated, based on an on-line update decision mechanism. The proposed channel pre-processing updater has been designed as a dedicated unit in a 65nm CMOS technology, resulting in a core area of 0.242mm2 (equivalent gate count of 116K). Running at a 330MHz clock, each QRD or R^-1 update consumes 4 or 2 times less energy compared to one exact state-of-the-art QRD in open literature.